IC73238: HOW TO DISABLE DIRECT I/O NEEDS TO BE DOCUMENTED

APAR status

• Closed as documentation error.

Error description

• Most file systems, by default, cache file data that is read from
  and written to disk.  Since the Tivoli Storage Manager server
  caches the data within the server this extra caching by the
  filesystem may cause performance degradation.  The Tivoli
  Storage Manager server will, by default, use non-buffered I/O
  bypassing the filesystem cache.
  
  In some cases, using non-buffered I/O might result in
  performance degradation.  In this case the server can be
  modified by an option to enable the usage of filesystem cache.
  Any performance tuning should be tested in a controlled
  environment before implementing it on a production system.
  
  DIRECTIO NO
  can be added to the server options file to disable the usage of
  non-buffered I/O.
  
  Initial Impact: Low
  
  Additional Keywords: TSM  zz61 zz62 XIV JFS2 GPFS
  

Local fix

• NOTE:  Any performance tuning should be tested in a controlled
  environment before implementing it on a production system.
  Add "DIRECTIO NO" to the TSM server option file and restart the
  TSM server.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All Tivoli Storage Manager server users.     *
  ****************************************************************
  * PROBLEM DESCRIPTION: See error description.                  *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  *
  

Problem conclusion

• Problem Conclusion:
  The following information, on using the DIRECTIO option, is
  included as a new topic in the Performance Tuning Guide:
  
  Enabling file system cache
  You can modify the server to use file system cache if the
  result is a significant performance improvement.
  
  Most file systems, by default, cache file data that is read
  from and written to disk. The Tivoli Storage Manager server
  caches data using non-buffered I/O, which bypasses the file
  system cache.
  
  For some environments, using non-buffered I/O might result
  in performance degradation. In these cases, the server can
  be modified to use file system cache.
  
  The DIRECTIO server option can be specified to control the
  use of non-buffered I/O. To disable non-buffered I/O, add
  DIRECTIO NO to the Tivoli Storage Manager server options
  file and restart the server.
  
  It is not recommended to disable non-buffered I/O unless
  it results in a significant improvement in performance.
  Using file system cache can decrease overall performance
  on some disk subsystems. Test all performance tuning in a
  controlled environment before implementing any changes on
  a production system.
  
  
  Affected platforms:
  AIX, HP-UX, Sun Solaris, Linux, and Windows
  

Temporary fix

Comments

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Fix information

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